It is proposed to use HeLa S3 cells and Physarum polycephalum in studies of the structure and composition of active chromatin and, in particular, the roles of histone acetylation and HMG proteins in chromosome structure. Ingram's finding that butyrate treatment of cells enhances histone acetylation will be used to obtain chromatin, oligomers of nucleosomes with enhanced levels of acetylation and separated acetylated histones. Physical and biochemical studies will be made of 1) the conformations and HMG protein contents of the 'acetylated' oligosomes compared with control oligosomes, 2) interactions and structures of specific complexes of highly acetylated histones, 3) reconstituted complexes from acetylated histones and either '140 bp DNA' or highly polymerized DNA. In P. polycephalum two copies of each of the genes for 26S, 19S and 5.8S ribosomal RNA are separated by a 30 kb spacer on a linear extrachromosomal palindromic 60 kb molecule. Restriction enzyme digestion separates the transcribed and spacer regions in free DNA and in nucleoli. The compositions and nuclease digestion of purified transcribed and non-transcribed chromatin regions will be studied. Histone acetylation and HMG proteins will be studied in detail through the precise, naturally synchronous nuclear division cycle of P. polycephalum. HMG proteins will be isolated from P. polycephalum, HeLa S3 and other tissues and their conformations and interactions with other components particularly acetylated states of chromatin will be studied by nuclease digestion and physical techniques.